The invention relates generally to communication systems and, more particularly, to a system and method for interconnecting Totem rings geographically separated by relatively long-distances.
A number of systems have been developed for providing network communications among groups of users. One such system comprises a Totem ring network in which a plurality of host processors, referred to herein as Totem servers, are connected to a bus network. Each Totem server includes circuitry for interfacing with the Totem ring network (e.g., sending and receiving messages on the Totem ring network), and a Central Processing Unit (CPU) adapted for executing processes comprising application programs effective for managing call processing, database operations, industrial control, and the like.
A Totem ring network provides for multicast delivery of messages, wherein messages may be transmitted and delivered to multiple locations, and ensures that the sequence in which messages are generated is maintained as such messages are transmitted and delivered throughout the system. Totem ring. networks are considered to be well-known to those skilled in the art and are described in greater detail in various technical papers and articles, such as an article entitled xe2x80x9cTotem: A Fault Tolerant Multicast Group Communication Systemxe2x80x9d by L. E. Moser et al., published in the April 1996, Vol. 39, No. 4 Edition of Communications of the ACM (Association for Computing Machinery).
Typically, Totem ring networks provide for totally ordered multicasting of messages over a single local area network (LAN), or multiple LANs in close proximity which are interconnected by devices referred to as gateways. Gateways, like routers in other network configurations, can be configured to function as Totem servers, described above, and are also effective for receiving communication packets on multiple interfaces and forwarding them to one or more destination interfaces. Gateways are typically configured with an off-the-shelf CPU and associated hardware and software which enable the gateway to interface with rings to which the gateway is connected.
The aforementioned sequence of messages and totally ordered multicasting of messages over a Totem ring network is maintained by protocols which attach timestamps and sequence numbers to each message. Errors are identified when such timestamps or sequence numbers are identified as being out of order.
Typically, a gateway on a Totem ring network forwards all messages it receives from one ring to all other rings to which it is connected, unless any such message has already been delivered to any such other ring. A drawback with Totem ring networks is that when Totem rings are geographically separated over long distances, as in wide area networks (WAN), at least one Totem ring must span a long distance, such as a mile or several hundreds of miles. The span of a single Totem ring over such long distances results in time latencies (such as a few tens of nanoseconds, or more) between servers on the Totem ring, which are sufficiently long to result in undesirable, and in many cases unacceptable, error rates on Totem rings. It can be appreciated, then, that time latencies limit the geographic size, and hence the capacity and utility, of Totem networks. Furthermore, as the operational speed of Totem ring networks increases in the future, such networks will become less tolerant to time latencies, thereby further limiting the geographic size, capacity, and utility of Totem networks.
Accordingly, a continuing search has been directed to the development of methods and systems which may enable Totem rings interconnected through a Totem ring network to be geographically separated over long distances without experiencing degradations in performance which result from long time latencies.
The present invention, accordingly, provides a Totem ring network with Totem rings which may be geographically separated by relatively long distances without experiencing degradations in performance. Time latencies between the geographically separated Totem rings are minimized by providing each of the geographically separated Totem rings with a router, and providing at least one point-to-point link interconnecting together the respective routers.
The present invention also provides a method for joining the geographically separated Totem rings of the Totem ring network by joining together, via at least one point-to-point link, the routers of the respective Totem rings.
The use of the present invention eliminates unacceptable latency time and resultant error rates between Totem rings which are separated by relatively long geographic distances. Thus, the geographic size, speed, capacity, and utility of Totem networks is significantly increased without incurring degradations in performance which result from long time latencies.